Last Updated: May 2026

You need to reduce the particle size of your industrial powder, but you have three different milling methods available and limited guidance on which one is right for your material. Choose the wrong method and you end up with the wrong particle size distribution, excessive heat buildup that degrades your product, inadequate throughput, or a tighter PSD than your process actually needs. So which method is right for your material, and what are the real differences between a Fitzmill, a hammer mill, and an air classifier mill?

Size reduction, also called comminution or milling, is the mechanical process of breaking solid particles from a larger size to a smaller, more controlled size range. In industrial chemical and polymer additive manufacturing, size reduction achieves a target particle size distribution that improves flowability, reactivity, blending uniformity, dissolution rate, or downstream processing performance. Toll Compaction operates three distinct technologies at its NJ and WV facilities: the Fitzmill, the Pulva hammer mill, and the air classifier mill. Each uses a different mechanical principle, which is why they perform differently across materials and target specifications.

The Fitzmill: Versatile Mid-Range Impact Milling

The Fitzmill is a rotating knife and screen mill that reduces particle size through a combination of impact, cutting, and attrition. Material enters the milling chamber where rotating blades strike and reduce particles. A screen at the outlet controls the maximum particle size. The Fitzmill can be configured with different blade types and screen sizes to target a wide range of particle sizes, and it operates at relatively low temperatures compared to hammer mills, making it suitable for moderately heat-sensitive materials.

Best for: mid-range particle size targets of approximately 150 to 2000 microns, friable or brittle materials, industrial chemicals, polymer additives, excipients, and food-grade powders. Also effective for de-agglomeration of caked or lumped powders.

The Pulva Hammer Mill: High-Energy Milling for Coarser Reduction

The hammer mill uses high-speed rotating hammers to impact and shatter particles against a breaker plate and screen. Toll Compaction’s Pulva hammer mill is a heavy-duty industrial mill designed for robust, high-throughput size reduction of harder or tougher materials. It generates more energy and impact force than a Fitzmill, making it suitable for materials requiring more aggressive reduction. The hammer mill operates at higher temperatures due to the energy of impact, so it is generally not the first choice for thermally sensitive materials.

Best for: coarse size reduction targets of approximately 500 to 5000 microns, hard or dense mineral and chemical materials, high-volume thermally stable industrial chemicals, and agricultural materials. Also used as a pre-reduction step before finer milling.

The Air Classifier Mill: Precision Fine Milling

The air classifier mill combines impact milling with an integrated air classification system that recirculates oversized particles back into the milling zone until they reach the target size. This closed-loop approach produces a much tighter, more controlled particle size distribution than either the Fitzmill or hammer mill, with a sharper upper particle size cutoff. The airflow through the system also carries heat away from the milling zone, making it more suitable for heat-sensitive polymer additives, organic chemicals, and food-grade materials.

Best for: fine particle size targets of approximately 10 to 150 microns, applications requiring a tight controlled distribution with a sharp upper cutoff, heat-sensitive polymer additives, organic chemicals, and high-value specialty materials where yield and minimal oversize are critical.

Side-by-Side Selection Guide

• Target particle size 500 to 5000 microns, hard or dense material: Hammer Mill
• Target particle size 150 to 2000 microns, friable or moderate hardness: Fitzmill
• Target particle size 10 to 150 microns, tight PSD required: Air Classifier Mill
• Material is thermally sensitive: Fitzmill or Air Classifier Mill
• High throughput is the priority: Hammer Mill
• Versatile, multi-product mid-range needs: Fitzmill
• Maximum PSD control with sharp upper cutoff: Air Classifier Mill

Key Questions to Guide Your Decision

• What is your target particle size range and how tight does the distribution need to be?
• Is your material thermally sensitive, and at what temperature does degradation begin?
• Is the material hard, brittle, friable, or fibrous?
• What is your required throughput and how does that affect cost per pound?
• Does your application require a sharp upper particle size cutoff?

Size Reduction as a Toll Processing Service

Many manufacturers do not own all three milling types and rely on toll processors for access to the right technology per product. Toll Compaction operates the Fitzmill, Pulva hammer mill, and air classifier mill at its NJ and WV facilities. We can run trial milling on small quantities before committing to production scale and provide particle size analysis with certificates of analysis on all finished material.

Need to reduce particle size on your powder? Contact Toll Compaction to discuss your target specification and material characteristics.